The present invention relates generally to structural latches for coupling apparatus for vehicles such as spacecraft, and is particularly concerned with a structural latch that is operable from the pressurizable side of the coupling apparatus and which is removable from the apparatus in the event the latch becomes inoperable or otherwise requires replacement. The invention relates further to the subject matter disclosed in our previously-filed Disclosure Document No. 185,822 entitled "Structural Latches For Spacecraft Docking/Berthing Mechanisms", which was filed in the United States Patent and Trademark Office on February 5, 1988.
Coupling apparatus offer a practical means for the mechanical joining, such as by berthing or docking, of spacecraft for the logistical support and transfer of crew members, for the mutual support of two or more spacecraft by a sharing of their individual facilities and capabilities, and for enabling the on-orbit assembly of spacecraft. Other on-orbit operations that require spacecraft to be docked include the structural expansion of spacecraft, the addition or exchange of modules containing expendable supplies and equipment needed for space-borne experiments and manufacturing processes, and the on-orbit repair and maintenance of spacecraft. Many of these operations are best implemented by crew members moving between the spacecraft in what is known as a "shirt-sleeve" environment, that is, in a pressurized, earth-like environment. The use of a properly designed coupling apparatus allows unrestricted passage of the crew between spacecraft without the need for cumbersome pressure suits.
In the art relating to vehicle coupling apparatus, a distinction exists between the terms "docking" and "berthing", although both terms describe the coupling of two or more spacecraft while on-orbit. The terms may be considered to characterize a difference in the manner in which the coupling is effected. To achieve a complete and successful coupling, the interfacing surfaces of the respective coupling apparatus must be fully coupled, or superimposed, by a force applied to the spacecraft. In berthing, the force is applied by a positioning system such as a manipulator arm carried by a neighboring spacecraft or one of the spacecraft to be joined. In docking, the force arises from the momentum imparted to the spacecraft to be coupled by propulsion means such as thrusters on one or both of the spacecraft. For the purposes of the following description, usage of the term "coupling" is meant to include both "docking" and "berthing" as well, unless the context clearly indicates otherwise.
Various types of apparatus have been proposed for accomplishing a temporary or permanent mechanical coupling between two or more spacecraft. A docking apparatus according to the prior art typically consists of a pair of complementary docking mechanisms, the first docking mechanism being attached to a port or opening of a first spacecraft and the second, complementary docking mechanism being attached to a similar port or opening of the second spacecraft. Each docking mechanism typically includes a flange which may be affixed to the port or opening of the spacecraft and is designed to encircle the aperture of the port. The flange is generally annular and is attached to the periphery of the port so as to provide for the unobstructed passage of crew members through the port aperture.
The docking mechanisms of the prior art first make contact with one another at their respective outer mating, or interface, surfaces during the course of a docking maneuver. Alignment guides at the periphery of each of the interface surfaces interdigitate with corresponding alignment guides carried by the complementary docking mechanism to correct slight rotational (clocking) misalignments of the mechanisms. Once the docking mechanisms are superposed over one another, they are mechanically joined by the operation of a plurality of complementary, hook-like structural latches. When the latches are fully engaged, the two spacecraft are locked together and provide a passage extending between the coupled spacecraft. Disengagement of the structural latches permits for uncoupling of the docking mechanisms and separation of the spacecraft from one another.
The hook-like structural latches of the prior art docking mechanisms extend from apertures spaced at even intervals around the circumference of the interface surface of each docking mechanism. The apertures of the respective docking mechanisms are alignable to permit interlocking of complementary hook-like latch elements. A plurality of motor-driven cams within one or both of the docking mechanisms are selectively actuable to extend and retract the hook-like devices to their respective apertures to permit coupling and disengagement of the respective docking mechanisms.
Structural latches have been operated on docking apparatus used in spaceflight during the Apollo program of the National Aeronautics and Space Administration (NASA) and on spacecraft developed and orbited by the Union of Soviet Socialist Republics (USSR). Such experience in the use of structural latches according to the prior art has shown them to be deficient in several aspects. As the structural latches are cam-driven, the components of the latch must be manufactured to precise tolerances and be adjusted periodically to ensure a proper engagement and retraction action between the respective docking mechanisms. A system of such complexity is therefore costly, mechanically complex, excessively heavy, and bulky. It is difficult to achieve consistent and reliable actuation of all of the latches because of the multiplicity of moving parts and because the parts are driven by one or more motors or other power devices. The motor drive requires close operator supervision and a complex control system for monitoring and preventing equipment malfunction, such as a jammed latch. In some instances, a malfunction can cause the motor drive to stall, which in turn can cease actuation of all other latches in the system, or in severe cases can damage or disable the motor drive and the jammed latch. In the event that one or more latches malfunction or fail to disengage when so commanded while on-orbit, an extensive effort is required to manually disengage them. Should latch disengagement from the interior of the spacecraft prove to be unsuccessful, an extra-vehicular activity may be necessary in order to effect the extrication and replacement of the failed latch.
Further NASA missions which require the use of a coupling apparatus are currently in the planning stage. In the near future, it is envisioned that the Space Transportation System (also referred to as the Space Shuttle Orbiter) developed in the United States by NASA will be used to service large, free-flying spacecraft, such as the proposed NASA Space Station and the Industrial Space Facility (ISF) developed by Space Industries Incorporated. Such spacecraft will be assembled and resupplied on orbit and will require vehicle coupling operations to be carried out on a frequent basis by the Space Transportation System. Therefore, relatively reliable structural latches will be required for use in coupling mechanisms carried by both the free-flying spacecraft and by the payload-carrying space vehicle in order to effect spacecraft coupling.
With respect to the Space Shuttle Orbiter, it is envisioned that this spacecraft will carry in its payload bay a coupling mechanism for engaging a similar coupling mechanism carried by another spacecraft. Because the payload bay of this spacecraft is positioned under a pair of selectively operable doors, the doors will have to be opened in order to provide the approaching spacecraft access to the coupling mechanism carried within the payload bay. Following disengagement and release of the spacecraft, the payload bay doors must be closed to permit the Space Shuttle Orbiter to re-enter the earth's atmosphere in a controlled manner. Therefore, a failure of the structural latches of the respective coupling mechanisms to disengage will prevent the release of the coupled spacecraft, thereby precluding closing of the payload bay doors. The inability to close the payload bay doors will severely jeopardize the mission and will preclude the return of the Space Shuttle Orbiter to earth.
Accordingly, an object of the present invention is to provide a structural latch which permits safe and reliable coupling operations to be conducted between two spacecraft.
Another object of the present invention is to provide a structural latch which is relatively simple in design, compact in size, lighter in weight, and less expensive to manufacture than known structural latch apparatus.
A further object of the present invention is to provide a structural latch that is manually operable, and which can be used to selectively couple and uncouple corresponding coupling mechanisms.
A further object of the present invention is to provide a structural latch which is readily removable and replaceable while spacecraft coupled thereby are on-orbit, the latch being removable without the necessity of time-consuming, extensive, or perilous procedures such as extra-vehicular excursions.